Summary: A quantitative formulation of the functional circuitry of the dorsal column nuclei, and measurement of the input-output relations for the nuclei are the central goals of this project. The use of computer simulation to generate and test hypotheses is also stressed. These goals indicate a need for quantitative experimental data about the system, including the definition of major cellular components and determination of their response properties as a function of variations in input parameters. Over the past several years the major outlines of the circuitry of the nuclei and the form of input-output relations for transmission and inhibition have been obtained. In the coming year these findings will be enlarged by examining input-output relations for single output elements, by extending computer simulations to include multi-population circuits and by measurement of input-output relations in awake animals.